In recent years, a virtualization function called Thin Provisioning has been the focus of attention as one of the functions that is installed in a storage apparatus. The Thin Provisioning function is a function which provides a virtual logical volume (hereinafter referred to as a virtual volume) to a host computer and for dynamically assigning storage areas to the virtual volume when a request to write data to the virtual volume is issued by the host computer. The Thin Provisioning function allows a virtual volume with a larger capacity than the storage area which can actually be provided to be provided to the host computer, and is advantageous in that a computer system can be constructed at low cost by reducing the physical storage capacity in the storage apparatus which is to be pre-prepared.
As a data management method of a storage apparatus with this built-in Thin Provisioning function, a hierarchical-type data management method has conventionally been proposed (PTL1, PTL2, for example). The hierarchical-type data management method is a method which manages storage areas provided by each of the storage devices of a plurality of types of varying performance which are installed in the storage apparatus as storage tiers of a plurality of different types, assigns storage areas from high-speed and high-performance storage tiers to areas in which data of a high access frequency in the virtual volume is stored, and assigns storage areas from low-speed and low-performance storage tiers to areas in which data of a low access frequency in the virtual volume is stored. This hierarchical-type data management method makes it possible to improve the cost performance of the storage apparatus.